Photographic material



Sept 11, 1945.

DENSITY DE/YS/ TY B. H. CARROLL 2,384,598

PHOTOGRAPHIC MATERIAL I Filed March 14, 1941 Fla.

Lbs EXPOSURE L06 EXPOSURE BURT/7. CARROLL NV T ATTORNEYS Patented Sept.El, 1945 UNITED STATES PATENT orrics amass PHOTOGBAPHIO MATERIAL Burt H.Carroll, Rochester, N. Y., mlgnor to Eastman Kodak Companmliochester, N.Y., a corporation of New Jersey Application March 14, 1941, Serial No.383,379

. 12 Claims. (01495-7) This invention relates to photographic materialand more particularly to photographic material which gives images ofdiilerent contrast under the same conditions of development.

It has been proposed to prepare photographic materials which give imagesof different contrast under the same conditions of development, byutilizing two independently prepared emulsions of different contrasts(either mixed together or coated in layers, one upon the other) andsensitizing one or both of the emulsions with sensitizing dyes, so thatthe composite emulsion re-' sponded difierently to light of differentwavelengths. As an example of this prior proposal, an emulsion whichworks hard (contrasty) and is sensitive to blue, such as a silverchloride emulsion, is mixed with an emulsion which works soft and issensitized to green, such as a spectrally sensitized silver bromideemulsion. Wh' n such a composite emulsion is exposed with light passedthrough a filter permeable only to green, the light which acts on thecontrasty emulsion is cut oil, and normal images can be made fromobjects of high contrast. Likewise, when such a composite emulsion isexposed with light passed through a filter permeable only to blue. thelight which acts on the "soft emulsion is cut 011, and;-

normal images can be made from objects of low contrast.

A variation of this prior proposal comprises spectrally sensitizing thecontrasty chloride emulsion to the green and leaving the "soft bromideemulsion free from spectral sensitizers, so that the contrasty emulsion,and not the soft" emulsion is afiected by light passed through a filterpermeable only to green.

I have now found that a' photographic material which respondsdifferently to light of different wavelengths and which gives images ofdifferent contrast under the same conditions of development, can mprepared with a single emulsion, instead of a composite of two or moredifferent emulsions. Thus, I have been able to avoid the undesirablefeatures of such a composite. By using a. single emulsion instead of acomposite of two difierent emulsions, the time of develop ment is moreconstant over the whole range oi contrasts, and a wider latitude inchoice of developers obtains. Moreover, if any addition (e. g. potassiumbromide) is made to the developing solution, the eflect thereof will bemorenearly the same over the whole range than when two difierentemulsions are involved.

It is accordingly an object of my invention to provide a photographicmaterial which gives images of different contrast under the sameconditions of development. A further object is to provide a process forpreparing such materials. Other objects will become apparenthereinafter.

In accordance with one embodiment of my invention, I take a silverhalide emulsion which may be of the chloride, chloriodide,chlorobromide, bromide or bromiodide type. of this emulsion, I take aportlonwhich is less than half and spectrally sensitize the portion (forexample, to the green) with -a sensitizing dye which does not wander ordifiuse in emulsions. I then thoroughly mix the spectrally sensitizedportion with the larger portion of the emulsion. If the so preparedemulsion is exposed through a blue filter, i. e., a filter permeableonly to blue light; it will be found to work hard, 1. e., to give normalimages of low contrast objects, while if it is exposed through aminusblue filter (Wratten N0. 12) it will be found to workisoft, i. e., togive normal images of high contrast objects. Advantageously the portionof the emulsion which I spectrally sensitize in practicing my inventionis equal to from about A; to about 5 of the volume of the totalemulsion. In practice, I have attained especially useful results byspectrally' sensitizingv about A of the silver halide particles.

. In accordance with a further embodiment of my invention, I take a.silver halide emulsion which can be any ofthe usual types indicatedabove. I take a portion of the' emulsion which is less than half andspectrally sensitize the portion- (for example to the red) with asensitizing dye which does not wander or difiuse in emulsions. I thentake the larger portion of the emulsion-and spectrally sensitize it tolight of a diiferent wavelength (for example, to the green) with asensitizing dye which does not wander or dlfiuse in emulsion. I thenthoroughly mix together the two portions of emulsion. If the sopreparedemulsion is exposed through a filterpermeable only to green light itwill be found to work hard, 1. e., to give normal images of low contrastobjects, while if it is exposed through a filter permeable only to redlight, it will work soft, i. e., give normal images of high contrastobjects. Advantageously, the portion of the emulsion which I spectrallysensitize to light of one wavelength is equal to from about to A, of thetotal volume of the emulsion, so that the portion of the emulsion whichis spectrally sensitized to light of another wavelength is from three toseven times as large. In practice, I have found that an emulsion, M 01'the particles of which are spectrally sensitized to light of onewavelength, and the remainder of the particles geously practiced withsensitizing dyes which are inherently non-diffusing. I have found thatirreversibility of adsorption ofthe sensitizing dyes to the silverhalide grains or -particles, i. e., lack of diffusion, can'be enh ced bydigesting the emulsion for some time th the sensitizing dye. Normally,sensitizing dyes arev incorporated in emulsion while the emulsions arein a liquid state, at about 30 to 35 C. I have found thatirreversibility of adsorption is enhanced by digesting at 40 C. or abovefor several minutes; for example, for about 15 minutes at 40 C. or forfrom into minutes at 50 C. In practicing my invention, it is veryimportant not to use excessive quantities of the sensitizing dyes, 1. efor the particles of silver halide, which it is intended should be dyed,the adsorptive capacity of the particles for dye should not be exceeded.Otherwise the unadsorbed excess dye will be adsorbed by the grains ofsilver halide which were intended to be free from dye, thereby ruiningthe effects obtained according to my'invention. Ordinarily, I have foundit advisable to employ concentrations of sensitizing dyes somewhat lessthan required to produce-optimum sensitization, i. e., within the rangefrom /2 of the optimum concentration up to the optimum. However, itshould be borne in mind that the best results are obtained in accordancewith my invention when all of the dyed silver halide particles haverather high sensitivity. Accordingly, I have found it advantageous toincorporate in those portions of the emulsion which I spectrallysensitize, substances which have a supersensitizing effect upon thesensitizing dyes.

The foregoing embodiments of my invention are not to be confused withthe so-cailed mixed grain color photographic emulsions where equal.instead of unequal, parts of an emulsion are treated to confer adifferent color sensitivity on each part.

'Non-diflusing sensitizing dyes which sensitize to the green are to befound in the thia-2'- cyanine, the benzothia-2'-cyanine, the selena-2'-cyanine, the 2,2'-cyanine, the thiazolo-2'-cyanine and thedibenzoxacarbocyanine classes of dyes. Non-diifusing dyes whichsensitize to longer wavelengths are to be found in thedibensothiacarbocyanine, the 5,5'- dichlorothiacarbocyanine, the 5chlorothiacarbocyauine, the 5 chlorothiaselenacarbocyanine, the fi-chlorothiabenzothiacarbocyanine, the 5,5 dichloroselenacarbocyanine,-th 5-chloroselenacarbocyanine, the 5-chloroselenathiacarbocyanine and the 5-chloroselenabenzothiacarbocyanineclasses of dyes. Non-diffusing sensitizing dyes are also to be foundamong the simple merocyanines, the merocarbocyanines and themerodicarbocyanines containing on the one hand a 3-alkylrhqdanine, a3-arylrhodanine or a 2-diarylamino-4(5) -thiazolone nucleus and on theother hand a benzoxazole, a benzothiazole, a benzoselenazole, anapthoxazole, anaphthothiazole, or a simple thiazole nucleus (1. e. athiazole nucleus devoid of a fused-on aromatic ring, e. g.i-methyl-thiazole and 4- phenylthiazole). Merocyanine dyes which containa long chain organic group (e. g. a 3-heptyl-'- l-phenyl-2-thiohydantoin nucleus) and which are especially resistant to diffusionare described in the copending application of Leslie G. 8.

Brooker, Serial No.,321,730, filed March 1, 1940' aseaeoe The followingexamples will serveto illustrate my invention.

Emmple 1 One liter of a cine positive gelatino-silveb bromiodideemulsion was divided into two portions of approximately 250 cc. and 750cc. "The 250 cc. portion was sensitized with,3.75 mg. of 2-methyl-l'-ethyl thia-2'-cyanine iodide by adding to the portionsufficient of a concentrated methyl alcoholic solutionof the dye to give3.75 mg.

After the dye was added to the portion, it was held at 50 C. for tenminutes. This spectrally sensitized portion was then thoroughly mixedwith the other portion of emulsion to which was added 1 mg. of1-(p-diethylaminostyryl) benzothiazole. The styryl compound, being adiffusing substance, passes from the silver halide grains which'are notspectraliy sensitized and superson- 250 cc. portion sitizes thesensitizing dye thereby increasing the speed of thosesilver halideparticles containing the sensitizing dye. Such supersensitization isdescribed in the copending application of B. 8. Carroll and J.A.'Leermakers, Serial No. 278,572, filed June 10. 1939 (-now U. 8.Patent 2,313,922, dated March 16, 1943). When an emulsion prepared asshown above was coated on a suitable support and allowed to dry and thenexposed through a blue filter which was found to have a speed of 7.25and a gamma of 1.97. On the other hand, when the emulsion was exposedthrough a minus blue filter (Wratten No. 12), it was found to have aspeed of 5.35 and a gamma of 0.97, under the same conditions ofdevelopment. In Figure 1 of the accompanying drawing, the char!acteristic curve for the exposure through the blue filter is shown bycurve A, and the characteristic curve for the exposure through the minusblue filter isshown by curve B. a If instead of adding 3.75 mg. of'2-methyi-1'- ethyl thia-2'-cyanine iodideto the 250 cc. portion only,the dye had been mixed with the whole liter of emulsion, the resultwould have been low speed and relatively high contrast in thegreen-sensitive region, with the poor gradation characteristic ofundersensitized emulsions as illustrated by the characteristic curve inFigure 2 of the accompanying drawing. In Figure 2, curve C is thecharacteristic curve of such an emulsion exposed through a blue filterand curve B is the characteristic curve of such an emulsion exposedthrough a minus blue fil v Emmple 2 One liter of a medium speedgelatino-silverbromiodide emulsion, such as can be used for reversalprocessing in color photography, was divided into portions of 250 cc.and 750 cc. The

was sensitized with 2.5 mg. of 2,2- dimethyl 8 ethyl 3',4,3',4'dibenzothiacarbocyanine bromide and the 750 cc. portion was sensitizedwith 20 mg. of 2,l'-diethyl-3,4-benzothia-2'-cyanine bromide. In eachcase, the dye was incorporated in the portion in the form of aconcentrated methyl alcoholic solution. In each (now U. S. patent2,282,116, dated May 5, 1M2). 0! my invention,Ispectrally sensitizeanemulsion.

emulsion was held for ten minutes at 50 C. after the addition of thesen- 4.7 and a gamma of 2.12.

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which can be any of the usual types indicated above, with a sensitizingdye which produces two sensitization maxima in the emulsion, one ofwhich tends to disappear as the concentration of the dye is increased.With such dyes, at some low concentration (considerably less than thatrequired for the normal optimum sensitization), maximum sensitizationwill btain at some wavelength, say in the green and if exposed withlight of about the wavelength of the region of maximum sensitivity, theemulsion will work hard. On the other hand, with such dyes at somehigher concentration (but still substantially less than that requiredfor normal optimum sensitization) a second sensitization maximum willobtain at some longer wavelength, say in the red, and if exposed withlight of about the wavelength of the region of such a second maximum,the emulsion will work soft. At this second concentration, then, theemulsion has two regions of maximum sensitivity, the one region givinghigh contrast and the other low. It is believed that the second maximumof sensitivity is caused by a new state of aggregation of-the dye on thesurface of the silver halide grains, and that an increasing number ofgrains are covered by the dye in this new state, as the concentration increases.

The sensitizing dyes which are employed in practicing this thirdembodiment of my invention need not be dyes which are resistant todiffusion. Moreover, the dyes may be added to the whole of the emulsion.The most useful concentration of dye will, of course, depend upon thenature of the dye and the nature of the emulsion. However, the mostuseful concentration of dye can readily be determined by sensitizing agiven emulsion with a series of concentrations of dye, beginning with arather low concentration, and

determining the sensitivity and contrast (gamma) of the emulsion in theusual manner. The following example will serve to illustrate the mannerof practicing this third embodiment of my invention.

Example 3 A cine positive gelatino-silver-bromiodide emulsion wassensitized with various concentrations 2,2 dimethyl8-ethyl-thiacarbocyanine iodide, using small test portions of theemulsion for each concentration. At the lowest concentrations, (0.2 to1.0 mg. of dye per liter of emulsion), the emulsion was sensitized onlyfor the green with a maximum at 560 mu. As the concentration of the dyewas increased, red sensitization appeared with a maximum at630 mu. At aconcentration of to 10 mg. of dye per liter of emulsion, the emulsionwhen exposed through a red (Wratten No. 25) filter had a speed of thesame order as through a blue (Wratten No. 47) filter, with a red light"nine dyes, especially those derived from 5-chlorobenzoselenazole, andthe meso alkyl substituted 5,5-dichloro-oxacarbocyanine dyes.

Practiced in accordance with any of the embodiments, my invention isprimarily directed to the customarily employed gelatino-silver-halidedeveloping-out emulsions. However, my inven-'' tions of development-itis possible to print sound.

and picture images at different and appropriate contrasts in cinepositive film. -What I claim as my invention and desire to be secured byLetters Patent of the United States is:

1. A process for preparing a photographic printing material for theproduction of images of diflerent contrast under the same conditions ofdevelopment comprising dividing a batch of one photographic silverhalide emulsion into two portions of unequal volume, one portionconstituting from about $4; to about $4; of the total volume of 7 thebatch, sensitizing the smaller portion with a sensitizing dye which doesnot wander from the silver halide grains so that the two portions oiemulsion are sensitized to diflerent spectral regions, and then mixingthe two portions of emulsion together.

2. A process for preparing a photographicprinting material for theproduction of images of diflerent contrast under the same conditions ofdevelopment comprising dividing a batch of gamma varying from M to ofthat of the blue light gamma. The main body of the emul ployed inpracticing this third embodiment of my invention are the meso alkyl"substituted thiacarbocyanine dyes, especially those derived from 5-chloro-benzothiazole and dialkylaminobenzothiazoles, the meso alkylsubstituted selenacarbocyaone photographic silver halide emulsion intotwo portions of unequal volume. one portion constituting about A of thetotal volume of the batch. sensitizing the smaller portion with asensitizing dye which does not wander from the silver halide grains sothat the twoportions of emulsion are sensitized to diii'er'ent spectralregions, and then mixing the two portions of emulsion together.

3. A process for preparing a photographic printing material for theproduction of images oi dinerent contrast under the same conditions ofdevelopment comprising dividing a batch of 'one photographic silverhalide emulsion intotwo portions of unequal volume, one portionconstituting from about V8 to about M; 01' the total volume of thebatch, sensitizing the smaller portion to the green with a sensitizingdye which does not wander from the silver halide grains, and then mixingthe two portions of emulsion together.

4. A process for preparing a photographic printing material for theproduction of images of different contrast under the same conditions ofdevelopment comprising dividing a batch of one photographic silverhalide emulsion into two portions 01' unequal volume, one portionconstituting about 01' the total volume of the batch, sensitizing thesmaller portion to the green with a sensitizing dye which does notwander from the silver halide grains, and then mixing the two portionsof emulsion together.

5. A process for preparing a photographic printing material for theproduction of images oi diiierent contrast under the same conditions ofdevelopment comprising dividing a-batch of one photographic silverhalide emulsion into two portions 01' unequal volume, one.portionconstituting from about it to about A oi the total volume oi thebatch, sensitizing the smaller portion to the red with a sensitizing dyewhich does not wander from the silver halide grains, sensitizing thelarger portion to the green with a sensitizing dye Y which does notwander from the silver halide printing material for the production ofimages of diiterent contrast under the same conditions of developmentcomprising dividing a batch of one photographic silver halide emulsioninto two po tions of unequal volume. one portion constituting about V ofthetotal volume of. the batch, sensitiling the smaller portion to thered with a sensitiling dye which does not wander from the silver halidegrains, sensitizing the larger portion to the green with a sensitizingdye which does not wander from the silver halide grains, and then mixingthe two portions of the .emulsion together.

7. A photographic printing material (or 'the production oi images ordiflerent contrast in the same emulsion layer under the same conditionsof development comprising a photographic silver halide emulsion layerwhich comprises a mixture of two portionsot unequal volume of the samebatch of photographic silver halide emulsion, one portion constitutingfrom about it to about V or the total volume of the batch. the smallerportion having been sensitised before mixing the portions with asensitizing dye which does not wander from the silver halide grains sothat the two portions of emulsion are sensitized to diii'erentspectralregions.

8. A photographic printing material for the production of images ofdiii'erent contrast in the same emulsion layer under the same conditionsof development comprising a photographic silver halide emulsion layerwhich comprises a mixture of'two portions of unequal volume of the samebatch of photographic silver halide emulsion, one portion constitutingabout V4 oi the total volume of the batch, the smaller portion havingbeen sensitized before mixing the portions with a sensitizing dye whichdom not wander from the silver halide grains so that the two portionsofemulsion are sensitized to diflerent spectral regions.

9. A photographic Printing material for the .production of images ofdiil'erent contrast in the same emulsion layer under the same conditionsof development comprising a photographic silver halide emulsion layerwhich comprises a mixture or two portions of unequal volume of-the samebatch of photographic silver halide emulsion, one

assesses v portion constituting from about it to about V4 01' the totalvolume of the batch. the smaller portion having been sensitized beforemixing the portions with a sensitizing dye which doesnot wander from thesilver halide grains so that the two portions of emulsion are sensitizedto diflerent spectral regions.

10. A photographic printing material for the production of'images ofdiiierent contrast in the same emulsion layer under the same conditionsI of development comprising a photographic silver halide'emulsion layerwhich comprises a mixture or two portions of unequal volume 01' the samebatch of photographic silver halide emulsion, one Portion constitutingabout V4 oi the total volume of the batch, the smaller portion havingbeen sensitized to the green before mixing the portions with asensitizing .dye which does not wander groin the silver halide grains sothat the two por- 20 ions of emulsion are sensitized to difl'erentspectral regions.

11. A photographic printing material for the production of images ofdifferent contrast in the same emulsion layer under the same conditionsof development comprising a photographic silver halide emulsion'layerwhich comprises a mixture of two portions of unequal .volume 01' thesame batch of photographic silver halide emulsion, one portionconstituting from about V to about V oi the total volume of the batch,the smaller portion having been sensitized to the red'before mixing theportions with a sensitizing dye which does not wander from the silverhalide grains and the larger portion having been sensitized to the greenbefore mixing the portions with a sensitizing dye which does not wanderfrom the silver halide stains.

12. A photographic printing material for the production of images ofdiiierent contrast in the same emulsion layer under the same conditionsof development comprising a photographic silver halide emulsion layerwhich comprises a mixture of two portions of unequal volume of the samebatch of photographic silver halide emulsions, one portion constitutingabout V4 of the total volume of the batch, the smaller portion havingbeen sensitized to the red before mixing the portions with a sensitizingdye which does not wander from the silver halide grains and the largerportion having been sensitized to the green before BURT-H. CARROLL.

